Gate-all-around integrated circuit structures having nanowires with tight vertical spacing

ABSTRACT

Gate-all-around integrated circuit structures having nanowires with tight vertical spacing, and methods of fabricating gate-all-around integrated circuit structures having nanowires with tight vertical spacing, are described. For example, an integrated circuit structure includes a vertical arrangement of horizontal silicon nanowires. A vertical spacing between vertically adjacent silicon nanowires is less than 6 nanometers. A gate stack is around the vertical arrangement of horizontal silicon nanowires. A first source or drain structure is at a first end of the vertical arrangement of horizontal silicon nanowires, and a second epitaxial source or drain structure is at a second end of the vertical arrangement of horizontal silicon nanowires.

TECHNICAL FIELD

Embodiments of the disclosure are in the field of integrated circuit structures and processing and, in particular, gate-all-around integrated circuit structures having nanowires with tight vertical spacing, and methods of fabricating gate-all-around integrated circuit structures having nanowires with tight vertical spacing.

BACKGROUND

For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory or logic devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant.

In the manufacture of integrated circuit devices, multi-gate transistors, such as tri-gate transistors, have become more prevalent as device dimensions continue to scale down. In conventional processes, tri-gate transistors are generally fabricated on either bulk silicon substrates or silicon-on-insulator substrates. In some instances, bulk silicon substrates are preferred due to their lower cost and because they enable a less complicated tri-gate fabrication process. In another aspect, maintaining mobility improvement and short channel control as microelectronic device dimensions scale below the 10 nanometer (nm) node provides a challenge in device fabrication. Nanowires used to fabricate devices provide improved short channel control.

Scaling multi-gate and nanowire transistors has not been without consequence, however. As the dimensions of these fundamental building blocks of microelectronic circuitry are reduced and as the sheer number of fundamental building blocks fabricated in a given region is increased, the constraints on the lithographic processes used to pattern these building blocks have become overwhelming. In particular, there may be a trade-off between the smallest dimension of a feature patterned in a semiconductor stack (the critical dimension) and the spacing between such features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate cross-sectional views representing various operations in a method of fabricating a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, in accordance with an embodiment of the present disclosure.

FIG. 2 illustrates a cross-sectional view representing a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, in accordance with an embodiment of the present disclosure.

FIG. 3 is a plot of increasing germanium (Ge) concentration as a function of increasing depth for two different silicon germanium layers deposited using different deposition conditions, in accordance with an embodiment of the present disclosure.

FIGS. 4A-4J illustrates cross-sectional views of various operations in a method of fabricating a gate-all-around integrated circuit structure, in accordance with an embodiment of the present disclosure.

FIG. 5 illustrates a cross-sectional view of a non-planar integrated circuit structure as taken along a gate line, in accordance with an embodiment of the present disclosure.

FIG. 6 illustrates cross-sectional views taken through nanowires and fins for a non-endcap architecture (left-hand side (a)) versus a self-aligned gate endcap (SAGE) architecture (right-hand side (b)), in accordance with an embodiment of the present disclosure.

FIG. 7 illustrates cross-sectional views representing various operations in a method of fabricating a self-aligned gate endcap (SAGE) structure with gate-all-around devices, in accordance with an embodiment of the present disclosure.

FIG. 8A illustrates a three-dimensional cross-sectional view of a nanowire-based integrated circuit structure, in accordance with an embodiment of the present disclosure.

FIG. 8B illustrates a cross-sectional source or drain view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the a-a′ axis, in accordance with an embodiment of the present disclosure.

FIG. 8C illustrates a cross-sectional channel view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the b-b′ axis, in accordance with an embodiment of the present disclosure.

FIG. 9 illustrates a computing device in accordance with one implementation of an embodiment of the disclosure.

FIG. 10 illustrates an interposer that includes one or more embodiments of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

Gate-all-around integrated circuit structures having nanowires with tight vertical spacing, and methods of fabricating gate-all-around integrated circuit structures having nanowires with tight vertical spacing, are described. In the following description, numerous specific details are set forth, such as specific integration and material regimes, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known features, such as integrated circuit design layouts, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be appreciated that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

Certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, and “side” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.

Embodiments described herein may be directed to front-end-of-line (FEOL) semiconductor processing and structures. FEOL is the first portion of integrated circuit (IC) fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) are patterned in the semiconductor substrate or layer. FEOL generally covers everything up to (but not including) the deposition of metal interconnect layers. Following the last FEOL operation, the result is typically a wafer with isolated transistors (e.g., without any wires).

Embodiments described herein may be directed to back-end of line (BEOL) semiconductor processing and structures. BEOL is the second portion of IC fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) are interconnected with wiring on the wafer, e.g., the metallization layer or layers. BEOL includes contacts, insulating layers (dielectrics), metal levels, and bonding sites for chip-to-package connections. In the BEOL part of the fabrication stage contacts (pads), interconnect wires, vias and dielectric structures are formed. For modern IC processes, more than 10 metal layers may be added in the BEOL.

Embodiments described below may be applicable to FEOL processing and structures, BEOL processing and structures, or both FEOL and BEOL processing and structures. In particular, although an example processing scheme may be illustrated using a FEOL processing scenario, such approaches may also be applicable to BEOL processing. Likewise, although an example processing scheme may be illustrated using a BEOL processing scenario, such approaches may also be applicable to FEOL processing.

One or more embodiments described herein are directed to gate-all-around transistors with silicon (Si) multiple nanowire transistors with tight vertical pitch, and methods of fabricating gate-all-around transistors with Si multiple nanowire transistors with tight vertical pitch.

To provide context, a limitation in the fabrication of Si nanowire/nanoribbon transistors on silicon substrates is the minimum vertical spacing of the wires. The vertical spacing may be limited by the interfacial abruptness of a silicon/silicon germanium (Si/SiGe) interface when a multilayer substrate stack is deposited. For typical process conditions where the width of the interface is approximately 3 nanometers, the minimum Si wire spacing is approximately 6 nanometers. For achieving a smaller vertical pitch, a more abrupt and stable interface may be needed. As such, a complication is the real-world limitations of interface abruptness. In order to scale the vertical distance between wires, the initial deposition of the substrate multilayer stack should be such that compositional abruptness supports very thin sacrificial material layers that are later removed to provide vertical separation of the nanowires and/or nanoribbons/nanosheets.

Previous nanowire or nanoribbon implementations involve the use of alternating wire and sacrificial layers having less abrupt interfaces. Such layers lead to a minimum wire (or ribbon or nanosheet) spacing of 6 nm or more. A gate stack formed thereon has a gate stack height that may be associated with parasitic capacitances and may also be more difficult to fabricate as it is made taller. Transistor current dictates that the stack be as many wires and as tall as possible. Embodiments of the present disclosure may be implemented to effectively squeeze the most performance from the relatively shortest gate stack height.

In accordance with one or more embodiments of the present disclosure, surface science techniques are employed to arrest adatom diffusion and suppress roughening and alloy surface segregation processes (where an adatom refers to an atom that lies on a crystal surface). Embodiments may be implemented by depositing sacrificial layers at relatively low temperatures (e.g., below 700 C), using appropriate precursors (e.g., high molecular weight silanes and/or germanes). In other embodiments, carbon is added to a sacrificial silicon germanium (SiGe) layer. The use of such additional diffusion suppression elements (such as C) may minimize thermal diffusion of Ge/Si.

Embodiments described herein may be suitable for 5 nm and smaller technology nodes for high performance nanowires/nanoribbons. Embodiments may be detected by the presence of silicon nanowires or ribbons or sheets with vertical spacing less than 6 nanometers in a finally fabricated device. In particular embodiments, a wide bottom gap is used for isolation allowing isolation on bulk Si wafers.

As an example process flow, FIGS. 1A-1C illustrate cross-sectional views representing various operations in a method of fabricating a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, in accordance with an embodiment of the present disclosure. FIG. 2 illustrates a cross-sectional view representing a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, in accordance with an embodiment of the present disclosure.

Referring to FIG. 1A, a starting structure includes an optional pristine epitaxial layer 104 formed on a substrate 102. In one embodiment, during processing, a silicon (Si) substrate 102 has a thin epitaxial silicon layer 104 formed thereon to provide a clean surface for subsequent silicon germanium epitaxial growth. In other embodiments, an epitaxial layer 104 is not formed. An optional relaxed buffer layer 106 may be grown on the optional pristine epitaxial layer 104. In an embodiment, the relaxed buffer layer 106 is a relaxed Si_(0.7)Ge_(0.3) layer.

Referring again to FIG. 1A, a sacrificial layer 108 is grown on the relaxed buffer layer 106. In an embodiment, the sacrificial layer 108 is a Si_(0.7)Ge_(0.3) layer. In one embodiment, the sacrificial layer 108 has a composition the same as or substantially the same as the relaxed buffer layer 106. In a particular embodiment, the sacrificial layer 108 is a Si_(0.7)Ge_(0.3) layer and the relaxed buffer layer 106 is a relaxed Si_(0.7)Ge_(0.3) layer. In one embodiment, the sacrificial layer 108 is formed by continuing growth relaxed buffer layer 106 in a same deposition process, and the sacrificial layer 108 and growth relaxed buffer layer 106 may appear as a unified layer. In another embodiment, the sacrificial layer 108 has a composition different from the relaxed buffer layer 106. Alternating channel layers 110 and intervening sacrificial layers 112 are formed on the sacrificial layer 108. In an embodiment, the channel layers 110 are silicon channel layers. In an embodiment, the intervening sacrificial layers 112 are intervening Si_(0.7)Ge_(0.3) layers.

In an embodiment, intervening sacrificial layers 112 are carbon-contaminated or carbon-doped. In one such embodiment, intervening sacrificial layers 112 are silicon germanium layers formed to include an amount of carbon suitable to suppress germanium diffusion between the silicon germanium intervening sacrificial layers 112 and the alternating silicon channel layers 110. In an embodiment, an amount of carbon the range of 0.1-5 atomic percent is used, with particular embodiments in the range of 0.5-1 atomic percent carbon in the silicon germanium layer. The carbon may be incorporated into the silicon germanium using high carbon content silicon and/or germanium precursors, such as high molecular weight silanes (e.g., disilane, trisilane, tetrasilane or higher silanes) and germanes (germane or digermane), and/or a specific carbon precursor (methyl silane or methane or ethane or acetylene or other alkane or alkene carbon containing molecule that may include silicon or germanium). It is to be appreciated that the sacrificial layer 108 underlying the multilayer stack may similarly be carbon-contaminated or carbon-doped, or may not be.

Referring to FIG. 1B, the stack of materials of FIG. 1A have a patterned mask 114/116 formed thereon, which may include a hardmask portion 116 and an etch stop portion 114. The patterned mask 114/116 is used to etch a plurality of fins in the stack of materials of FIG. 1A. In an embodiment, the etching is deeper than the optional pristine epitaxial layer 104. In one such embodiment, each fin includes a patterned substrate portion 122, a pristine epitaxial layer 124, an optional relaxed buffer layer 126, a sacrificial layer 128, channel layers 130, an intervening sacrificial layers 132.

Referring to FIG. 1C, isolation structures 134, such as shallow trench isolation structures, are formed between fins. It is to be appreciated that the height of the isolation structures 134 may be selected depending on the processing used or the application targeted. Although the height of the isolation structures 134 is depicted as relatively low in FIG. 1C, in other embodiments, the height of the isolation structures 134 may be substantially higher in the case that isolated (and not merged) devices are fabricated.

Referring again to FIG. 1C, dummy gate structures are then formed over the fins and over the isolation structures 134. Each of the dummy gate structures includes a dummy gate electrode 146, a hardmask 148, sidewall spacers 150, and a dielectric helmet 152. A dummy gate dielectric may also be included beneath the dummy gate electrode 146, as is depicted. In one embodiment, the dummy gate dielectric is a remnant of the mask layer 114.

Referring again to FIG. 1C, the dummy gate structures are used as a mask to etch trenches into exposed portions of the fins, e.g., into source and drain regions of the fins. The etching removes portions of channel layers 130 to form channel layers 140, and removes portions of the intervening sacrificial layers 132 to form intervening sacrificial layers 142. In one embodiment, the etching extends at least partially into sacrificial layer 128 to form recessed sacrificial layer 138 having trenches formed therein. Epitaxial source or drain structures 144 may then be grown in the trenches. It is to be appreciated that in the example embodiment depicted in FIG. 1C, the epitaxial source or drain structures 144 are shown as merged. In other embodiments, the epitaxial source or drain structures 144 are not merged, enabling the fabrication of discrete adjacent devices. In such embodiments, the isolation structures 134 may be taller than the embodiment depicted.

Referring to FIG. 2 , following source/drain deposition, the dummy gate electrode 146 and the sacrificial layers 142 are removed. In an embodiment, the formation of a carbon-contaminated or carbon-doped silicon germanium intervening sacrificial layers 112 (to ultimately provide sacrificial layers 142) enables control over the spacing between silicon channel layers 140 upon release of the silicon channel layers 140 by removal of the intervening sacrificial layers 142. For example, a carbon-contaminated or carbon-doped silicon germanium intervening sacrificial layer 112 can be formed to a thickness less than 6 nanometers, and a vertical spacing of less than 6 nanometers is maintained between released silicon channel layers 140 (such as between 2 and 5 nanometers). In an embodiment, a carbon coating, carbon-based coating, or a coating containing carbon remains as a residue on the silicon channel layers 140 following removal of the sacrificial layers 142.

FIG. 3 is a plot 300 of increasing germanium (Ge) concentration as a function of increasing depth for two different silicon germanium layers deposited using different deposition conditions, in accordance with an embodiment of the present disclosure. Profile 302 represents a silicon germanium layer without carbon content. The profile 302 has a Ge content with a central profile that tapers off relatively quickly, effectively indicating a thicker sacrificial layer/nanowire interface resulting in less control over spacing of resulting nanowires once released. Profile 302 represents a silicon germanium layer with poor composition abruptness. The profile 304 has a Ge content with a central profile that is broader and less tapered, effectively enabling a thinner sacrificial layer/nanowire interface resulting in greater control over spacing of resulting nanowires once released, enabling formation of tighter spacing between vertically adjacent nanowires.

Referring again to FIG. 2 , the removed sacrificial layers 142 (as seen in FIG. 1C) are replaced with a permanent gate electrode 170 and gate dielectric stack 172. In one embodiment, the gate electrode 170 is a metal gate electrode, and the gate dielectric 172 is a high-k gate dielectric. In an embodiment, a portion of the recessed sacrificial layer 138 is further recessed in the gate channel region to form a gate electrode 170 in a further recessed sacrificial layer 158, where the gate electrode 170 is deeper than the epitaxial source or drain structures 144, as is depicted. In an embodiment, portions 162 of the sacrificial layers 142 are retained on either side of the gate electrode 170, as is also depicted. In an embodiment, a contact barrier layer 174 and conductive fill 176 are formed over the epitaxial source or drain structures 144. It is to be appreciated that the structure of FIG. 2 may be further planarized in order to confine the permanent gate electrode 170 to the gate locations.

With reference again to FIG. 2 , in accordance with an embodiment of the present disclosure, an integrated circuit structure includes a vertical arrangement of horizontal silicon nanowires 140. A gate stack 170/172 is around the vertical arrangement of horizontal silicon nanowires 140. A first source or drain structure 144 is at a first end of the vertical arrangement of horizontal silicon nanowires 140, and a second epitaxial source or drain structure 144 is at a second end of the vertical arrangement of horizontal silicon nanowires 140. In an embodiment, a vertical spacing between vertically adjacent silicon nanowires 140 is less than 6 nanometers, e.g., between 2 and 5 nanometers. In an embodiment, one or more of the silicon nanowires 140 has a coating including carbon.

In an embodiment, the vertical arrangement of horizontal silicon nanowires 140 is above a fin. In one embodiment, a vertical spacing between the fin and a bottommost silicon nanowire 140 of the vertical arrangement of horizontal silicon nanowires 140 is greater than the vertical spacing between vertically adjacent silicon nanowires 140. In one embodiment, the fin includes a portion of a bulk silicon substrate.

In an embodiment, the first and second epitaxial source or drain structures 144 are non-discrete first and second epitaxial source or drain structures, as is depicted. In another embodiment, the first and second epitaxial source or drain structures 144 are discrete first and second epitaxial source or drain structures, an example of which is described below in association with FIGS. 4A-4J. In an embodiment, the first and second epitaxial source or drain structures 144 are compressive-stressing source or drain structures, e.g., epitaxial silicon germanium source or drain structures for silicon nanowires or nanoribbons. In another embodiment, the first and second epitaxial source or drain structures 144 are tensile-stressing source or drain structures, e.g., epitaxial carbon-doped silicon source or drain structures for silicon nanowires or nanoribbons.

As used throughout, a silicon layer may be used to describe a silicon material composed of a very substantial amount of, if not all, silicon. However, it is to be appreciated that, practically, 100% pure Si may be difficult to form and, hence, could include a small percentage of carbon, germanium or tin. Such impurities may be included as an unavoidable impurity or component during deposition of Si or may “contaminate” the Si upon diffusion during post deposition processing. As such, embodiments described herein directed to a silicon layer may include a silicon layer that contains a relatively small amount, e.g., “impurity” level, non-Si atoms or species, such as Ge, Sn or C. It is to be appreciated that a silicon layer as described herein may be undoped or may be doped with dopant atoms such as boron, phosphorous or arsenic.

As used throughout, a silicon germanium layer may be used to describe a silicon germanium material composed of substantial portions of both silicon and germanium, such as at least 5% of both. In some embodiments, the amount of germanium is greater than the amount of silicon. In particular embodiments, a silicon germanium layer includes approximately 60% germanium and approximately 40% silicon (Si_(0.4)Ge_(0.6)). In other embodiments, the amount of silicon is greater than the amount of germanium. In particular embodiments, a silicon germanium layer includes approximately 30% germanium and approximately 70% silicon (Si_(0.7)Ge_(0.3)). It is to be appreciated that, practically, 100% pure silicon germanium (referred to generally as SiGe) may be difficult to form and, hence, could include a tiny percentage of carbon or tin. Such impurities may be included as an unavoidable impurity or component during deposition of SiGe or may “contaminate” the SiGe upon diffusion during post deposition processing. As such, embodiments described herein directed to a silicon germanium layer may include a silicon germanium layer that contains a relatively small amount, e.g., “impurity” level, non-Ge and non-Si atoms or species, such as carbon or tin. It is to be appreciated that a silicon germanium layer as described herein may be undoped or may be doped with dopant atoms such as boron, phosphorous or arsenic.

In some embodiments, a silicon germanium layer is formed to include an amount of carbon greater than an amount otherwise considered unavoidable or “impurity” level of carbon. For example, in some embodiments, a suitable amount of carbon is included in a silicon germanium layer to suppress diffusion between the silicon germanium layer and an adjacent silicon layer. In an embodiment, an amount of carbon the range of 0.1-5 atomic percent of the silicon germanium layer is used, with particular embodiments in the range of 0.5-1 atomic percent carbon in the silicon germanium layer. The carbon may be incorporated into the silicon germanium using high carbon content silicon and/or germanium precursors, or a specific carbon precursor.

In another aspect, nanowire release processing may be performed through a replacement gate trench. Examples of such release processes are described below. Additionally, in yet another aspect, backend (BE) interconnect scaling can result in lower performance and higher manufacturing cost due to patterning complexity. Embodiments described herein may be implemented to enable front-side and back-side interconnect integration for nanowire transistors. Embodiments described herein may provide an approach to achieve a relatively wider interconnect pitch. The result may be improved product performance and lower patterning costs. Embodiments may be implemented to enable robust functionality of scaled nanowire or nanoribbon transistors with low power and high performance.

One or more embodiments described herein are directed dual epitaxial (EPI) connections for nanowire or nanoribbon transistors using partial source or drain (SD) and asymmetric trench contact (TCN) depth. In an embodiment, an integrated circuit structure is fabricated by forming source-drain openings of nanowire/nanoribbon transistors which are partially filled with SD epitaxy. A remainder of the opening is filled with a conductive material. Deep trench formation on one of the source or drain side enables direct contact to a back-side interconnect level. In a particular embodiment, source or drain structures are formed as nubs in order to provide space for contact formation. The source or drain nubs may or may not be stressing on their own. If not, in combination with an adjacent contact material, such source or drain nubs may be stressing for associated channel regions. In another embodiment, source or drain semiconductor material fills the recess in a more conventional approach.

In an example process flow including the fabrication of source or drain nubs, FIGS. 4A-4J illustrates cross-sectional views of various operations in a method of fabricating a gate-all-around integrated circuit structure, in accordance with an embodiment of the present disclosure.

Referring to FIG. 4A, a method of fabricating an integrated circuit structure includes forming a starting stack, which includes alternating sacrificial layers 404 and nanowires 406 above a fin 402, such as a silicon fin. The nanowires 406 may be referred to as a vertical arrangement of nanowires. A protective cap 408 may be formed above the alternating sacrificial layers 404 and nanowires 406, as is depicted. A relaxed buffer layer 452 and a pristine epitaxial layer 450 may be formed beneath the alternating sacrificial layers 404 and nanowires 406, as is also depicted.

Referring to FIG. 4B, a gate stack 410 is formed over the vertical arrangement of horizontal nanowires 406. Portions of the vertical arrangement of horizontal nanowires 406 are then released by removing portions of the sacrificial layers 404 to provide recessed sacrificial layers 404′ and cavities 412, as is depicted in FIG. 4C. In an embodiment, the sacrificial layers 404 include silicon germanium with carbon to act as a germanium diffusion suppressant, and the released horizontal nanowires 406 have a relatively tighter vertical pitch, as described above.

It is to be appreciated that the structure of FIG. 4C may be fabricated to completion without first performing the deep etch and asymmetric contact processing described below, e.g., to provide all top-side contact structures. In either case (e.g., with or without asymmetric contact processing), in an embodiment, a fabrication process involves use of a process scheme that provides a gate-all-around integrated circuit structure having epitaxial nubs, which may be vertically discrete source or drain structures.

Referring to FIG. 4D, upper gate spacers 414 are formed at sidewalls of the gate structure 410. Cavity spacers 416 are formed in the cavities 412 beneath the upper gate spacers 414. A deep trench contact etch is then optionally performed to form trenches 418 and to form recessed nanowires 406′. A sacrificial material 420 is then formed in the trenches 418, as is depicted in FIG. 4E. In other process schemes, an isolated trench bottom or silicon trench bottom may be used. In an embodiment, relaxed buffer layer 452 and pristine epitaxial layer 450 become patterned relaxed buffer layer 452′ and patterned pristine epitaxial layer 450′, as is depicted.

Referring to FIG. 4F, a first epitaxial source or drain structure (e.g., left-hand features 422) is formed at a first end of the vertical arrangement of horizontal nanowires 406′. A second epitaxial source or drain structure (e.g., right-hand features 422) is formed at a second end of the vertical arrangement of horizontal nanowires 406′. In an embodiment, as depicted, the epitaxial source or drain structures 422 are vertically discrete source or drain structures and may be referred to as epitaxial nubs. In an embodiment, the epitaxial source or drain structures are silicon germanium source or drain structures or carbon-doped silicon source or drain structures.

An inter-layer dielectric (ILD) material 424 is then formed at the sides of the gate electrode 410 and adjacent the source or drain structures 422, as is depicted in FIG. 4G. Referring to FIG. 4H, a replacement gate process is used to form a permanent gate dielectric 428 and a permanent gate electrode 426. The ILD material 424 is then removed, as is depicted in FIG. 4I. The sacrificial material 420 is then removed from one of the source drain locations (e.g., right-hand side) to form trench 432, but is not removed from the other of the source drain locations to form trench 430.

Referring to FIG. 4J, a first conductive contact structure 434 is formed coupled to the first epitaxial source or drain structure (e.g., left-hand features 422). A second conductive contact structure 436 is formed coupled to the second epitaxial source or drain structure (e.g., right-hand features 422). The second conductive contact structure 436 is formed deeper along the fin 402 than the first conductive contact structure 434. In an embodiment, although not depicted in FIG. 4J, the method further includes forming an exposed surface of the second conductive contact structure 436 at a bottom of the fin 402. Conductive contacts may include a contact resistance reducing layer and a primary contact electrode layer, where examples can include Ti, Ni, Co for the former and W, Ru, Co for the latter.

In an embodiment, the second conductive contact structure 436 is deeper along the fin 402 than the first conductive contact structure 434, as is depicted. In one such embodiment, the first conductive contact structure 434 is not along the fin 402, as is depicted. In another such embodiment, not depicted, the first conductive contact structure 434 is partially along the fin 402.

In an embodiment, the second conductive contact structure 436 is along an entirety of the fin 402. In an embodiment, although not depicted, in the case that the bottom of the fin 402 is exposed by a back-side substrate removal process, the second conductive contact structure 436 has an exposed surface at a bottom of the fin 402.

In another aspect, in order to enable access to both conductive contact structures of a pair of asymmetric source and drain contact structures, integrated circuit structures described herein may be fabricated using a back-side reveal of front-side structures fabrication approach. In some example embodiments, reveal of the back-side of a transistor or other device structure entails wafer-level back-side processing. In contrast to a conventional TSV-type technology, a reveal of the back-side of a transistor as described herein may be performed at the density of the device cells, and even within sub-regions of a device. Furthermore, such a reveal of the back-side of a transistor may be performed to remove substantially all of a donor substrate upon which a device layer was disposed during front-side device processing. As such, a microns-deep TSV becomes unnecessary with the thickness of semiconductor in the device cells following a reveal of the back-side of a transistor potentially being only tens or hundreds of nanometers.

Reveal techniques described herein may enable a paradigm shift from “bottom-up” device fabrication to “center-out” fabrication, where the “center” is any layer that is employed in front-side fabrication, revealed from the back-side, and again employed in back-side fabrication. Processing of both a front-side and revealed back-side of a device structure may address many of the challenges associated with fabricating 3D ICs when primarily relying on front-side processing.

A reveal of the back-side of a transistor approach may be employed for example to remove at least a portion of a carrier layer and intervening layer of a donor-host substrate assembly. The process flow begins with an input of a donor-host substrate assembly. A thickness of a carrier layer in the donor-host substrate is polished (e.g., CMP) and/or etched with a wet or dry (e.g., plasma) etch process. Any grind, polish, and/or wet/dry etch process known to be suitable for the composition of the carrier layer may be employed. For example, where the carrier layer is a group IV semiconductor (e.g., silicon), a CMP slurry known to be suitable for thinning the semiconductor may be employed. Likewise, any wet etchant or plasma etch process known to be suitable for thinning the group IV semiconductor may also be employed.

In some embodiments, the above is preceded by cleaving the carrier layer along a fracture plane substantially parallel to the intervening layer. The cleaving or fracture process may be utilized to remove a substantial portion of the carrier layer as a bulk mass, reducing the polish or etch time needed to remove the carrier layer. For example, where a carrier layer is 400-900 μm in thickness, 100-700 μm may be cleaved off by practicing any blanket implant known to promote a wafer-level fracture. In some example embodiments, a light element (e.g., H, He, or Li) is implanted to a uniform target depth within the carrier layer where the fracture plane is desired. Following such a cleaving process, the thickness of the carrier layer remaining in the donor-host substrate assembly may then be polished or etched to complete removal. Alternatively, where the carrier layer is not fractured, the grind, polish and/or etch operation may be employed to remove a greater thickness of the carrier layer.

Next, exposure of an intervening layer is detected. Detection is used to identify a point when the back-side surface of the donor substrate has advanced to nearly the device layer. Any endpoint detection technique known to be suitable for detecting a transition between the materials employed for the carrier layer and the intervening layer may be practiced. In some embodiments, one or more endpoint criteria are based on detecting a change in optical absorbance or emission of the back-side surface of the donor substrate during the polishing or etching performed. In some other embodiments, the endpoint criteria are associated with a change in optical absorbance or emission of byproducts during the polishing or etching of the donor substrate back-side surface. For example, absorbance or emission wavelengths associated with the carrier layer etch byproducts may change as a function of the different compositions of the carrier layer and intervening layer. In other embodiments, the endpoint criteria are associated with a change in mass of species in byproducts of polishing or etching the back-side surface of the donor substrate. For example, the byproducts of processing may be sampled through a quadrupole mass analyzer and a change in the species mass may be correlated to the different compositions of the carrier layer and intervening layer. In another example embodiment, the endpoint criteria is associated with a change in friction between a back-side surface of the donor substrate and a polishing surface in contact with the back-side surface of the donor substrate.

Detection of the intervening layer may be enhanced where the removal process is selective to the carrier layer relative to the intervening layer as non-uniformity in the carrier removal process may be mitigated by an etch rate delta between the carrier layer and intervening layer. Detection may even be skipped if the grind, polish and/or etch operation removes the intervening layer at a rate sufficiently below the rate at which the carrier layer is removed. If an endpoint criteria is not employed, a grind, polish and/or etch operation of a predetermined fixed duration may stop on the intervening layer material if the thickness of the intervening layer is sufficient for the selectivity of the etch. In some examples, the carrier etch rate:intervening layer etch rate is 3:1-10:1, or more.

Upon exposing the intervening layer, at least a portion of the intervening layer may be removed. For example, one or more component layers of the intervening layer may be removed. A thickness of the intervening layer may be removed uniformly by a polish, for example. Alternatively, a thickness of the intervening layer may be removed with a masked or blanket etch process. The process may employ the same polish or etch process as that employed to thin the carrier, or may be a distinct process with distinct process parameters. For example, where the intervening layer provides an etch stop for the carrier removal process, the latter operation may employ a different polish or etch process that favors removal of the intervening layer over removal of the device layer. Where less than a few hundred nanometers of intervening layer thickness is to be removed, the removal process may be relatively slow, optimized for across-wafer uniformity, and more precisely controlled than that employed for removal of the carrier layer. A CMP process employed may, for example, employ a slurry that offers very high selectively (e.g., 100:1-300:1, or more) between semiconductor (e.g., silicon) and dielectric material (e.g., SiO) surrounding the device layer and embedded within the intervening layer, for example, as electrical isolation between adjacent device regions.

For embodiments where the device layer is revealed through complete removal of the intervening layer, back-side processing may commence on an exposed back-side of the device layer or specific device regions there in. In some embodiments, the back-side device layer processing includes a further polish or wet/dry etch through a thickness of the device layer disposed between the intervening layer and a device region previously fabricated in the device layer, such as a source or drain region.

In some embodiments where the carrier layer, intervening layer, or device layer back-side is recessed with a wet and/or plasma etch, such an etch may be a patterned etch or a materially selective etch that imparts significant non-planarity or topography into the device layer back-side surface. As described further below, the patterning may be within a device cell (i.e., “intra-cell” patterning) or may be across device cells (i.e., “inter-cell” patterning). In some patterned etch embodiments, at least a partial thickness of the intervening layer is employed as a hard mask for back-side device layer patterning. Hence, a masked etch process may preface a correspondingly masked device layer etch.

The above described processing scheme may result in a donor-host substrate assembly that includes IC devices that have a back-side of an intervening layer, a back-side of the device layer, and/or back-side of one or more semiconductor regions within the device layer, and/or front-side metallization revealed. Additional back-side processing of any of these revealed regions may then be performed during downstream processing.

It is to be appreciated that the structures resulting from the above example processing schemes may be used in a same or similar form for subsequent processing operations to complete device fabrication, such as PMOS and/or NMOS device fabrication. As an example of a completed device, FIG. 5 illustrate a cross-sectional view of a non-planar integrated circuit structure as taken along a gate line, in accordance with an embodiment of the present disclosure.

Referring to FIG. 5 , a semiconductor structure or device 500 includes a non-planar active region (e.g., a fin structure including protruding fin portion 504 and sub-fin region 505) within a trench isolation region 506. In an embodiment, instead of a solid fin, the non-planar active region is separated into nanowires (such as nanowires 504A and 504B) above sub-fin region 505, as is represented by the dashed lines. In either case, for ease of description for non-planar integrated circuit structure 500, a non-planar active region 504 is referenced below as a protruding fin portion. In an embodiment, the sub-fin region 505 also includes a relaxed buffer layer 592 and a pristine epitaxial layer 590, as is depicted. In an embodiment, a fabrication process involves use of a process scheme that provides a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, which may be silicon nanowires with tight vertical spacing such as described in association with FIGS. 1A-1C and 2 .

A gate line 508 is disposed over the protruding portions 504 of the non-planar active region (including, if applicable, surrounding nanowires 504A and 504B), as well as over a portion of the trench isolation region 506. As shown, gate line 508 includes a gate electrode 550 and a gate dielectric layer 552. In one embodiment, gate line 508 may also include a dielectric cap layer 554. A gate contact 514, and overlying gate contact via 516 are also seen from this perspective, along with an overlying metal interconnect 560, all of which are disposed in inter-layer dielectric stacks or layers 570. Also seen from the perspective of FIG. 5 , the gate contact 514 is, in one embodiment, disposed over trench isolation region 506, but not over the non-planar active regions. In another embodiment, the gate contact 514 is over the non-planar active regions.

In an embodiment, the semiconductor structure or device 500 is a non-planar device such as, but not limited to, a fin-FET device, a tri-gate device, a nanoribbon device, or a nanowire device. In such an embodiment, a corresponding semiconducting channel region is composed of or is formed in a three-dimensional body. In one such embodiment, the gate electrode stacks of gate lines 508 surround at least a top surface and a pair of sidewalls of the three-dimensional body.

As is also depicted in FIG. 5 , in an embodiment, an interface 580 exists between a protruding fin portion 504 and sub-fin region 505. The interface 580 can be a transition region between a doped sub-fin region 505 and a lightly or undoped upper fin portion 504. In one such embodiment, each fin is approximately 10 nanometers wide or less, and sub-fin dopants are optionally supplied from an adjacent solid state doping layer at the sub-fin location. In a particular such embodiment, each fin is less than 10 nanometers wide. However, in other embodiments, fins as wide as 50 nm for example are used for nanoribbon fabrication.

Although not depicted in FIG. 5 , it is to be appreciated that source or drain regions of or adjacent to the protruding fin portions 504 are on either side of the gate line 508, i.e., into and out of the page. In one embodiment, the material of the protruding fin portions 504 in the source or drain locations is removed and replaced with another semiconductor material, e.g., by epitaxial deposition to form epitaxial source or drain structures. The source or drain regions may extend below the height of dielectric layer of trench isolation region 506, i.e., into the sub-fin region 505. In accordance with an embodiment of the present disclosure, the more heavily doped sub-fin regions, i.e., the doped portions of the fins below interface 580, inhibits source to drain leakage through this portion of the bulk semiconductor fins. In an embodiment, the source and drain regions have associated asymmetric source and drain contact structures, as described above in association with FIG. 4J. With reference again to FIG. 5 , in an embodiment, fins 504/505 (and, possibly nanowires 504A and 504B) are composed of a crystalline silicon layer which may be doped with a charge carrier, such as but not limited to phosphorus, arsenic, boron, gallium or a combination thereof.

In an embodiment, trench isolation region 506, and trench isolation regions (trench isolations structures or trench isolation layers) described throughout, may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, portions of a permanent gate structure from an underlying bulk substrate or isolate active regions formed within an underlying bulk substrate, such as isolating fin active regions. For example, in one embodiment, trench isolation region 506 is composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride.

Gate line 508 may be composed of a gate electrode stack which includes a gate dielectric layer 552 and a gate electrode layer 550. In an embodiment, the gate electrode of the gate electrode stack is composed of a metal gate and the gate dielectric layer is composed of a high-k material. For example, in one embodiment, the gate dielectric layer is composed of a material such as, but not limited to, hafnium oxide, hafnium oxy-nitride, hafnium silicate, lanthanum oxide, zirconium oxide, zirconium silicate, tantalum oxide, barium strontium titanate, barium titanate, strontium titanate, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zinc niobate, or a combination thereof. Furthermore, a portion of gate dielectric layer may include a layer of native oxide formed from the top few layers of the substrate fin 504. In an embodiment, the gate dielectric layer is composed of a top high-k portion and a lower portion composed of an oxide of a semiconductor material. In one embodiment, the gate dielectric layer is composed of a top portion of hafnium oxide and a bottom portion of silicon dioxide or silicon oxy-nitride. In some implementations, a portion of the gate dielectric is a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate.

In one embodiment, the gate electrode is composed of a metal layer such as, but not limited to, metal nitrides, metal carbides, metal silicides, metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt, nickel or conductive metal oxides. In a specific embodiment, the gate electrode is composed of a non-workfunction-setting fill material formed above a metal workfunction-setting layer. The gate electrode layer may consist of a P-type workfunction metal or an N-type workfunction metal, depending on whether the transistor is to be a PMOS or an NMOS transistor. In some implementations, the gate electrode layer may consist of a stack of two or more metal layers, where one or more metal layers are workfunction metal layers and at least one metal layer is a conductive fill layer. For a PMOS transistor, metals that may be used for the gate electrode include, but are not limited to, ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, e.g., ruthenium oxide. A P-type metal layer will enable the formation of a PMOS gate electrode with a workfunction that is between about 4.9 eV and about 5.2 eV. For an NMOS transistor, metals that may be used for the gate electrode include, but are not limited to, hafnium, zirconium, titanium, tantalum, aluminum, alloys of these metals, and carbides of these metals such as hafnium carbide, zirconium carbide, titanium carbide, tantalum carbide, and aluminum carbide. An N-type metal layer will enable the formation of an NMOS gate electrode with a workfunction that is between about 3.9 eV and about 4.2 eV. In some implementations, the gate electrode may consist of a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate. In another implementation, at least one of the metal layers that form the gate electrode may simply be a planar layer that is substantially parallel to the top surface of the substrate and does not include sidewall portions substantially perpendicular to the top surface of the substrate. In further implementations of the disclosure, the gate electrode may consist of a combination of U-shaped structures and planar, non-U-shaped structures. For example, the gate electrode may consist of one or more U-shaped metal layers formed atop one or more planar, non-U-shaped layers.

Spacers associated with the gate electrode stacks may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, a permanent gate structure from adjacent conductive contacts, such as self-aligned contacts. For example, in one embodiment, the spacers are composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride.

Gate contact 514 and overlying gate contact via 516 may be composed of a conductive material. In an embodiment, one or more of the contacts or vias are composed of a metal species. The metal species may be a pure metal, such as tungsten, nickel, or cobalt, or may be an alloy such as a metal-metal alloy or a metal-semiconductor alloy (e.g., such as a silicide material).

In an embodiment (although not shown), a contact pattern which is essentially perfectly aligned to an existing gate line 508 is formed while eliminating the use of a lithographic step with exceedingly tight registration budget. In an embodiment, the contact pattern is a vertically symmetric contact pattern, or an asymmetric contact pattern such as described in association with FIG. 4J. In other embodiments, all contacts are front-side connected and are not asymmetric. In one such embodiment, the self-aligned approach enables the use of intrinsically highly selective wet etching (e.g., versus conventionally implemented dry or plasma etching) to generate contact openings. In an embodiment, a contact pattern is formed by utilizing an existing gate pattern in combination with a contact plug lithography operation. In one such embodiment, the approach enables elimination of the need for an otherwise critical lithography operation to generate a contact pattern, as used in conventional approaches. In an embodiment, a trench contact grid is not separately patterned, but is rather formed between poly (gate) lines. For example, in one such embodiment, a trench contact grid is formed subsequent to gate grating patterning but prior to gate grating cuts.

In an embodiment, providing structure 500 involves fabrication of the gate stack structure 508 by a replacement gate process. In such a scheme, dummy gate material such as polysilicon or silicon nitride pillar material, may be removed and replaced with permanent gate electrode material. In one such embodiment, a permanent gate dielectric layer is also formed in this process, as opposed to being carried through from earlier processing. In an embodiment, dummy gates are removed by a dry etch or wet etch process. In one embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a dry etch process including use of SF₆. In another embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a wet etch process including use of aqueous NH₄OH or tetramethylammonium hydroxide. In one embodiment, dummy gates are composed of silicon nitride and are removed with a wet etch including aqueous phosphoric acid.

Referring again to FIG. 5 , the arrangement of semiconductor structure or device 500 places the gate contact over isolation regions. Such an arrangement may be viewed as inefficient use of layout space. In another embodiment, however, a semiconductor device has contact structures that contact portions of a gate electrode formed over an active region, e.g., over a fin 505, and in a same layer as a trench contact via.

It is to be appreciated that not all aspects of the processes described above need be practiced to fall within the spirit and scope of embodiments of the present disclosure. Also, the processes described herein may be used to fabricate one or a plurality of semiconductor devices. The semiconductor devices may be transistors or like devices. For example, in an embodiment, the semiconductor devices are a metal-oxide semiconductor (MOS) transistors for logic or memory, or are bipolar transistors. Also, in an embodiment, the semiconductor devices have a three-dimensional architecture, such as a tri-gate device, an independently accessed double gate device, or a FIN-FET. One or more embodiments may be particularly useful for fabricating semiconductor devices at a sub-10 nanometer (10 nm) technology node.

In an embodiment, as used throughout the present description, interlayer dielectric (ILD) material is composed of or includes a layer of a dielectric or insulating material. Examples of suitable dielectric materials include, but are not limited to, oxides of silicon (e.g., silicon dioxide (SiO₂)), doped oxides of silicon, fluorinated oxides of silicon, carbon doped oxides of silicon, various low-k dielectric materials known in the arts, and combinations thereof. The interlayer dielectric material may be formed by conventional techniques, such as, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), or by other deposition methods.

In an embodiment, as is also used throughout the present description, metal lines or interconnect line material (and via material) is composed of one or more metal or other conductive structures. A common example is the use of copper lines and structures that may or may not include barrier layers between the copper and surrounding ILD material. As used herein, the term metal includes alloys, stacks, and other combinations of multiple metals. For example, the metal interconnect lines may include barrier layers (e.g., layers including one or more of Ta, TaN, Ti or TiN), stacks of different metals or alloys, etc. Thus, the interconnect lines may be a single material layer, or may be formed from several layers, including conductive liner layers and fill layers. Any suitable deposition process, such as electroplating, chemical vapor deposition or physical vapor deposition, may be used to form interconnect lines. In an embodiment, the interconnect lines are composed of a conductive material such as, but not limited to, Cu, Al, Ti, Zr, Hf, V, Ru, Co, Ni, Pd, Pt, W, Ag, Au or alloys thereof. The interconnect lines are also sometimes referred to in the art as traces, wires, lines, metal, or simply interconnect.

In an embodiment, as is also used throughout the present description, hardmask materials, capping layers, or plugs are composed of dielectric materials different from the interlayer dielectric material. In one embodiment, different hardmask, capping or plug materials may be used in different regions so as to provide different growth or etch selectivity to each other and to the underlying dielectric and metal layers. In some embodiments, a hardmask layer, capping or plug layer includes a layer of a nitride of silicon (e.g., silicon nitride) or a layer of an oxide of silicon, or both, or a combination thereof. Other suitable materials may include carbon-based materials. Other hardmask, capping or plug layers known in the arts may be used depending upon the particular implementation. The hardmask, capping or plug layers maybe formed by CVD, PVD, or by other deposition methods.

In an embodiment, as is also used throughout the present description, lithographic operations are performed using 193 nm immersion lithography (i193), EUV and/or EBDW lithography, or the like. A positive tone or a negative tone resist may be used. In one embodiment, a lithographic mask is a trilayer mask composed of a topographic masking portion, an anti-reflective coating (ARC) layer, and a photoresist layer. In a particular such embodiment, the topographic masking portion is a carbon hardmask (CHM) layer and the anti-reflective coating layer is a silicon ARC layer.

In another aspect, one or more embodiments are directed to neighboring semiconductor structures or devices separated by self-aligned gate endcap (SAGE) structures. Particular embodiments may be directed to integration of multiple width (multi-Wsi) nanowires and nanoribbons in a SAGE architecture and separated by a SAGE wall. In an embodiment, nanowires/nanoribbons are integrated with multiple Wsi in a SAGE architecture portion of a front-end process flow. Such a process flow may involve integration of nanowires and nanoribbons of different Wsi to provide robust functionality of next generation transistors with low power and high performance. Associated epitaxial source or drain regions may be embedded (e.g., portions of nanowires removed and then source or drain (S/D) growth is performed).

To provide further context, advantages of a self-aligned gate endcap (SAGE) architecture may include the enabling of higher layout density and, in particular, scaling of diffusion to diffusion spacing. To provide illustrative comparison, FIG. 6 illustrates cross-sectional views taken through nanowires and fins for a non-endcap architecture (left-hand side (a)) versus a self-aligned gate endcap (SAGE) architecture (right-hand side (b)), in accordance with an embodiment of the present disclosure.

Referring to the left-hand side (a) of FIG. 6 , an integrated circuit structure 600 includes a substrate 602 having fins 604 protruding therefrom by an amount 606 above an isolation structure 608 laterally surrounding lower portions of the fins 604. Upper portions of the fins may include a relaxed buffer layer 622 and a pristine epitaxial layer 620, as is depicted. Corresponding nanowires 605 are over the fins 604. A gate structure may be formed over the integrated circuit structure 600 to fabricate a device. However, breaks in such a gate structure may be accommodated for by increasing the spacing between fin 604/nanowire 605 pairs.

By contrast, referring to the right-hand side (b) of FIG. 6 , an integrated circuit structure 650 includes a substrate 652 having fins 654 protruding therefrom by an amount 656 above an isolation structure 658 laterally surrounding lower portions of the fins 654. Upper portions of the fins may include a relaxed buffer layer 672 and a pristine epitaxial layer 670, as is depicted. Corresponding nanowires 655 are over the fins 654. Isolating SAGE walls 660 (which may include a hardmask thereon, as depicted) are included within the isolation structure 652 and between adjacent fin 654/nanowire 655 pairs. The distance between an isolating SAGE wall 660 and a nearest fin 654/nanowire 655 pair defines the gate endcap spacing 662. A gate structure may be formed over the integrated circuit structure 650, between insolating SAGE walls to fabricate a device. Breaks in such a gate structure are imposed by the isolating SAGE walls. Since the isolating SAGE walls 660 are self-aligned, restrictions from conventional approaches can be minimized to enable more aggressive diffusion to diffusion spacing. Furthermore, since gate structures include breaks at all locations, individual gate structure portions may be layer connected by local interconnects formed over the isolating SAGE walls 660. In an embodiment, as depicted, the SAGE walls 660 each include a lower dielectric portion and a dielectric cap on the lower dielectric portion. In accordance with an embodiment of the present disclosure, a fabrication process for structures associated with FIG. 6 involves use of a process scheme that provides a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, which may be silicon nanowires with tight vertical spacing such as described in association with FIGS. 1A-1C and 2 .

A self-aligned gate endcap (SAGE) processing scheme involves the formation of gate/trench contact endcaps self-aligned to fins without requiring an extra length to account for mask mis-registration. Thus, embodiments may be implemented to enable shrinking of transistor layout area. Embodiments described herein may involve the fabrication of gate endcap isolation structures, which may also be referred to as gate walls, isolation gate walls or self-aligned gate endcap (SAGE) walls.

In an example processing scheme for structures having SAGE walls separating neighboring devices, FIG. 7 illustrate cross-sectional views representing various operations in a method of fabricating a self-aligned gate endcap (SAGE) structure with gate-all-around devices, in accordance with an embodiment of the present disclosure.

Referring to part (a) of FIG. 7 , a starting structure includes a nanowire patterning stack 704 above a substrate 702. A lithographic patterning stack 706 is formed above the nanowire patterning stack 704. The nanowire patterning stack 704 includes alternating sacrificial layers 710 and nanowire layers 712, which may be above a relaxed buffer layer 782 and a pristine epitaxial layer 780, as is depicted. A protective mask 714 is between the nanowire patterning stack 704 and the lithographic patterning stack 706. In one embodiment, the lithographic patterning stack 706 is trilayer mask composed of a topographic masking portion 720, an anti-reflective coating (ARC) layer 722, and a photoresist layer 724. In a particular such embodiment, the topographic masking portion 720 is a carbon hardmask (CHM) layer and the anti-reflective coating layer 722 is a silicon ARC layer.

Referring to part (b) of FIG. 7 , the stack of part (a) is lithographically patterned and then etched to provide an etched structure including trenches 730.

Referring to part (c) of FIG. 7 , the structure of part (b) has an isolation layer 740 and a SAGE material 742 formed in trenches 730. The structure is then planarized to leave patterned topographic masking layer 720′ as an exposed upper layer.

Referring to part (d) of FIG. 7 , the isolation layer 740 is recessed below an upper surface of the patterned substrate 702, e.g., to define a protruding fin portion and to provide a trench isolation structure 741 beneath SAGE walls 742.

Referring to part (e) of FIG. 7 , the sacrificial layers 710 are removed at least in the channel region to release nanowires 712A and 712B. Subsequent to the formation of the structure of part (e) of FIG. 7 , a gate stacks may be formed around nanowires 712B or 712A, over protruding fins of substrate 702, and between SAGE walls 742. In one embodiment, prior to formation of the gate stacks, the remaining portion of protective mask 714 is removed. In another embodiment, the remaining portion of protective mask 714 is retained as an insulating fin hat as an artifact of the processing scheme.

Referring again to part (e) of FIG. 7 , it is to be appreciated that a channel view is depicted, with source or drain regions (such as epitaxial source or drain regions) being locating into and out of the page. In an embodiment, the channel region including nanowires 712B has a width less than the channel region including nanowires 712A. Thus, in an embodiment, an integrated circuit structure includes multiple width (multi-Wsi) nanowires. Although structures of 712B and 712A may be differentiated as nanowires and nanoribbons, respectively, both such structures are typically referred to herein as nanowires. It is also to be appreciated that reference to or depiction of a fin/nanowire pair throughout may refer to a structure including a fin and one or more overlying nanowires (e.g., two overlying nanowires are shown in FIG. 7 ). In accordance with an embodiment of the present disclosure, a fabrication process for structures associated with FIG. 7 involves use of a process scheme that provides a gate-all-around integrated circuit structure having nanowires with tight vertical spacing, which may be silicon nanowires with tight vertical spacing such as described in association with FIGS. 1A-1C and 2 .

In an embodiment, as described throughout, self-aligned gate endcap (SAGE) isolation structures may be composed of a material or materials suitable to ultimately electrically isolate, or contribute to the isolation of, portions of permanent gate structures from one another. Example materials or material combinations include a single material structure such as silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride. Other example materials or material combinations include a multi-layer stack having lower portion silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride and an upper portion higher dielectric constant material such as hafnium oxide.

To highlight an example integrated circuit structure having three vertically arranged nanowires, FIG. 8A illustrates a three-dimensional cross-sectional view of a nanowire-based integrated circuit structure, in accordance with an embodiment of the present disclosure. FIG. 8B illustrates a cross-sectional source or drain view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the a-a′ axis. FIG. 8C illustrates a cross-sectional channel view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the b-b′ axis.

Referring to FIG. 8A, an integrated circuit structure 800 includes one or more vertically stacked nanowires (804 set) above a substrate 802. In an embodiment, as depicted, a relaxed buffer layer 802C, a pristine epitaxial layer 802B, and a lower substrate portion 802A are included in substrate 802, as is depicted. An optional fin below the bottommost nanowire and formed from the substrate 802 is not depicted for the sake of emphasizing the nanowire portion for illustrative purposes. Embodiments herein are targeted at both single wire devices and multiple wire devices. As an example, a three nanowire-based devices having nanowires 804A, 804B and 804C is shown for illustrative purposes. For convenience of description, nanowire 804A is used as an example where description is focused on one of the nanowires. It is to be appreciated that where attributes of one nanowire are described, embodiments based on a plurality of nanowires may have the same or essentially the same attributes for each of the nanowires.

Each of the nanowires 804 includes a channel region 806 in the nanowire. The channel region 806 has a length (L). Referring to FIG. 8C, the channel region also has a perimeter (Pc) orthogonal to the length (L). Referring to both FIGS. 8A and 8C, a gate electrode stack 808 surrounds the entire perimeter (Pc) of each of the channel regions 806. The gate electrode stack 808 includes a gate electrode along with a gate dielectric layer between the channel region 806 and the gate electrode (not shown). In an embodiment, the channel region is discrete in that it is completely surrounded by the gate electrode stack 808 without any intervening material such as underlying substrate material or overlying channel fabrication materials. Accordingly, in embodiments having a plurality of nanowires 804, the channel regions 806 of the nanowires are also discrete relative to one another.

Referring to both FIGS. 8A and 8B, integrated circuit structure 800 includes a pair of non-discrete source or drain regions 810/812. The pair of non-discrete source or drain regions 810/812 is on either side of the channel regions 806 of the plurality of vertically stacked nanowires 804. Furthermore, the pair of non-discrete source or drain regions 810/812 is adjoining for the channel regions 806 of the plurality of vertically stacked nanowires 804. In one such embodiment, not depicted, the pair of non-discrete source or drain regions 810/812 is directly vertically adjoining for the channel regions 806 in that epitaxial growth is on and between nanowire portions extending beyond the channel regions 806, where nanowire ends are shown within the source or drain structures. In another embodiment, as depicted in FIG. 8A, the pair of non-discrete source or drain regions 810/812 is indirectly vertically adjoining for the channel regions 806 in that they are formed at the ends of the nanowires and not between the nanowires. In an embodiment, the non-discrete source or drain regions 810/812 are non-discrete silicon germanium or carbon-doped silicon source or drain regions.

In an embodiment, as depicted, the source or drain regions 810/812 are non-discrete in that there are not individual and discrete source or drain regions for each channel region 806 of a nanowire 804. Accordingly, in embodiments having a plurality of nanowires 804, the source or drain regions 810/812 of the nanowires are global or unified source or drain regions as opposed to discrete for each nanowire. That is, the non-discrete source or drain regions 810/812 are global in the sense that a single unified feature is used as a source or drain region for a plurality (in this case, 3) of nanowires 804 and, more particularly, for more than one discrete channel region 806. In one embodiment, from a cross-sectional perspective orthogonal to the length of the discrete channel regions 806, each of the pair of non-discrete source or drain regions 810/812 is approximately rectangular in shape with a bottom tapered portion and a top vertex portion, as depicted in FIG. 8B. In other embodiments, however, the source or drain regions 810/812 of the nanowires are relatively larger yet discrete non-vertically merged epitaxial structures such as nubs described in association with FIGS. 4A-4J.

In accordance with an embodiment of the present disclosure, and as depicted in FIGS. 8A and 8B, integrated circuit structure 800 further includes a pair of contacts 814, each contact 814 on one of the pair of non-discrete source or drain regions 810/812. In one such embodiment, in a vertical sense, each contact 814 completely surrounds the respective non-discrete source or drain region 810/812. In another aspect, the entire perimeter of the non-discrete source or drain regions 810/812 may not be accessible for contact with contacts 814, and the contact 814 thus only partially surrounds the non-discrete source or drain regions 810/812, as depicted in FIG. 8B. In a contrasting embodiment, not depicted, the entire perimeter of the non-discrete source or drain regions 810/812, as taken along the a-a′ axis, is surrounded by the contacts 814.

Referring again to FIG. 8A, in an embodiment, integrated circuit structure 800 further includes a pair of spacers 816. As is depicted, outer portions of the pair of spacers 816 may overlap portions of the non-discrete source or drain regions 810/812, providing for “embedded” portions of the non-discrete source or drain regions 810/812 beneath the pair of spacers 816. As is also depicted, the embedded portions of the non-discrete source or drain regions 810/812 may not extend beneath the entirety of the pair of spacers 816.

In an embodiment, the nanowires 804 may be sized as wires or ribbons, as described below, and may have squared-off or rounder corners. In an embodiment, the nanowires 804 are composed of silicon. In one such embodiment, the nanowires are single-crystalline. For example, for a silicon nanowire 804, a single-crystalline nanowire may be based from a (100) global orientation, e.g., with a <100> plane in the z-direction. As described below, other orientations may also be considered. In an embodiment, the dimensions of the nanowires 804, from a cross-sectional perspective, are on the nano-scale. For example, in a specific embodiment, the smallest dimension of the nanowires 804 is less than approximately 20 nanometers. In some embodiments, nanowires 804 have a width in the range of 5-20 nm (e.g., for wires). In some embodiments, nanowires 804 have a width in the range of 20-80 nm (e.g., for ribbons). In an embodiment, the nanowires 804 are composed of a strained material, particularly in the channel regions 806.

The structure 800 may be fabricated from a starting semiconductor-on-insulator substrate. Alternatively, the structure 800 is formed directly from a bulk substrate and local oxidation is used to form electrically insulative portions in place of the above described upper insulator layer. In another alternative embodiment, the structure 800 is formed directly from a bulk substrate and doping is used to form electrically isolated active regions, such as nanowires, thereon. In one such embodiment, the first nanowire (i.e., proximate the substrate) is in the form of an omega-FET type structure.

Referring to FIGS. 8C, in an embodiment, each of the channel regions 806 has a width (Wc) and a height (Hc), the width (Wc) approximately the same as the height (Hc). That is, in both cases, the channel regions 806 are square-like or, if corner-rounded, circle-like in cross-section profile. In another aspect, the width and height of the channel region need not be the same, such as the case for nanoribbons as described throughout. In an embodiment, channel regions 806 have tight vertical spacing, which may be silicon channel regions with tight vertical spacing such as described in association with FIGS. 1A-1C and 2 .

In an embodiment, as described throughout, an integrated circuit structure includes non-planar devices such as, but not limited to, a finFET or a tri-gate device with corresponding one or more overlying nanowire structures. In such an embodiment, a corresponding semiconducting channel region is composed of or is formed in a three-dimensional body with one or more discrete nanowire channel portions overlying the three-dimensional body. In one such embodiment, the gate structures surround at least a top surface and a pair of sidewalls of the three-dimensional body, and further surrounds each of the one or more discrete nanowire channel portions.

In an embodiment, as described throughout, an underlying substrate may be composed of a semiconductor material that can withstand a manufacturing process and in which charge can migrate. In an embodiment, the substrate is a bulk substrate composed of a crystalline silicon, silicon/germanium or germanium layer doped with a charge carrier, such as but not limited to phosphorus, arsenic, boron, gallium or a combination thereof, to form an active region. In one embodiment, the concentration of silicon atoms in a bulk substrate is greater than 97%. In another embodiment, a bulk substrate is composed of an epitaxial layer grown atop a distinct crystalline substrate, e.g. a silicon epitaxial layer grown atop a boron-doped bulk silicon mono-crystalline substrate. A bulk substrate may alternatively be composed of a group III-V material. In an embodiment, a bulk substrate is composed of a III-V material such as, but not limited to, gallium nitride, gallium phosphide, gallium arsenide, indium phosphide, indium antimonide, indium gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, or a combination thereof. In one embodiment, a bulk substrate is composed of a III-V material and the charge-carrier dopant impurity atoms are ones such as, but not limited to, carbon, silicon, germanium, oxygen, sulfur, selenium or tellurium.

Embodiments disclosed herein may be used to manufacture a wide variety of different types of integrated circuits and/or microelectronic devices. Examples of such integrated circuits include, but are not limited to, processors, chipset components, graphics processors, digital signal processors, micro-controllers, and the like. In other embodiments, semiconductor memory may be manufactured. Moreover, the integrated circuits or other microelectronic devices may be used in a wide variety of electronic devices known in the arts. For example, in computer systems (e.g., desktop, laptop, server), cellular phones, personal electronics, etc. The integrated circuits may be coupled with a bus and other components in the systems. For example, a processor may be coupled by one or more buses to a memory, a chipset, etc. Each of the processor, the memory, and the chipset, may potentially be manufactured using the approaches disclosed herein.

FIG. 9 illustrates a computing device 900 in accordance with one implementation of an embodiment of the present disclosure. The computing device 900 houses a board 902. The board 902 may include a number of components, including but not limited to a processor 904 and at least one communication chip 906. The processor 904 is physically and electrically coupled to the board 902. In some implementations the at least one communication chip 906 is also physically and electrically coupled to the board 902. In further implementations, the communication chip 906 is part of the processor 904.

Depending on its applications, computing device 900 may include other components that may or may not be physically and electrically coupled to the board 902. These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth).

The communication chip 906 enables wireless communications for the transfer of data to and from the computing device 900. The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip 906 may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The computing device 900 may include a plurality of communication chips 906. For instance, a first communication chip 906 may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip 906 may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

The processor 904 of the computing device 900 includes an integrated circuit die packaged within the processor 904. The integrated circuit die of the processor 904 may include one or more structures, such as gate-all-around integrated circuit structures having nanowires with tight vertical spacing built in accordance with implementations of embodiments of the present disclosure. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory.

The communication chip 906 also includes an integrated circuit die packaged within the communication chip 906. The integrated circuit die of the communication chip 906 may include one or more structures, such as gate-all-around integrated circuit structures having nanowires with tight vertical spacing built in accordance with implementations of embodiments of the present disclosure.

In further implementations, another component housed within the computing device 900 may contain an integrated circuit die that includes one or structures, such as gate-all-around integrated circuit structures having nanowires with tight vertical spacing built in accordance with implementations of embodiments of the present disclosure.

In various implementations, the computing device 900 may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, the computing device 900 may be any other electronic device that processes data.

FIG. 10 illustrates an interposer 1000 that includes one or more embodiments of the present disclosure. The interposer 1000 is an intervening substrate used to bridge a first substrate 1002 to a second substrate 1004. The first substrate 1002 may be, for instance, an integrated circuit die. The second substrate 1004 may be, for instance, a memory module, a computer motherboard, or another integrated circuit die. Generally, the purpose of an interposer 1000 is to spread a connection to a wider pitch or to reroute a connection to a different connection. For example, an interposer 1000 may couple an integrated circuit die to a ball grid array (BGA) 1006 that can subsequently be coupled to the second substrate 1004. In some embodiments, the first and second substrates 1002/1004 are attached to opposing sides of the interposer 1000. In other embodiments, the first and second substrates 1002/1004 are attached to the same side of the interposer 1000. And, in further embodiments, three or more substrates are interconnected by way of the interposer 1000.

The interposer 1000 may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In further implementations, the interposer 1000 may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-V and group IV materials.

The interposer 1000 may include metal interconnects 1008 and vias 1010, including but not limited to through-silicon vias (TSVs) 1012. The interposer 1000 may further include embedded devices 1014, including both passive and active devices. Such devices include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, and electrostatic discharge (ESD) devices. More complex devices such as radio-frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and MEMS devices may also be formed on the interposer 1000. In accordance with embodiments of the disclosure, apparatuses or processes disclosed herein may be used in the fabrication of interposer 1000 or in the fabrication of components included in the interposer 1000.

Thus, embodiments of the present disclosure include gate-all-around integrated circuit structures having nanowires with tight vertical spacing, and methods of fabricating gate-all-around integrated circuit structures nanowires with tight vertical spacing.

The above description of illustrated implementations of embodiments of the disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. While specific implementations of, and examples for, the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize.

These modifications may be made to the disclosure in light of the above detailed description. The terms used in the following claims should not be construed to limit the disclosure to the specific implementations disclosed in the specification and the claims. Rather, the scope of the disclosure is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Example embodiment 1: An integrated circuit structure includes a vertical arrangement of horizontal silicon nanowires. A vertical spacing between vertically adjacent silicon nanowires is less than 6 nanometers. A gate stack is around the vertical arrangement of horizontal silicon nanowires. A first source or drain structure is at a first end of the vertical arrangement of horizontal silicon nanowires, and a second epitaxial source or drain structure is at a second end of the vertical arrangement of horizontal silicon nanowires.

Example embodiment 2: The integrated circuit structure of example embodiment 1, wherein the vertical arrangement of horizontal silicon nanowires is above a fin.

Example embodiment 3: The integrated circuit structure of example embodiment 2, wherein a vertical spacing between the fin and a bottommost silicon nanowire of the vertical arrangement of horizontal silicon nanowires is greater than the vertical spacing between vertically adjacent silicon nanowires.

Example embodiment 4: The integrated circuit structure of example embodiment 2 or 3, wherein the fin comprises a portion of a bulk silicon substrate.

Example embodiment 5: The integrated circuit structure of example embodiment 1, 2, 3 or 4, wherein the first and second source or drain structures are first and second epitaxial source or drain structures.

Example embodiment 6: The integrated circuit structure of example embodiment 5, wherein the first and second epitaxial source or drain structures comprise silicon and germanium.

Example embodiment 7: The integrated circuit structure of example embodiment 5 or 6, wherein the first and second epitaxial source or drain structures are non-discrete first and second epitaxial source or drain structures.

Example embodiment 8: The integrated circuit structure of example embodiment 5 or 6, wherein the first and second epitaxial source or drain structures are discrete first and second epitaxial source or drain structures.

Example embodiment 9: The integrated circuit structure of example embodiment 1, 2, 3, 4, 5, 6, 7 or 8, wherein the gate stack includes a high-k gate dielectric layer and a metal gate electrode.

Example embodiment 10: The integrated circuit structure of example embodiment 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein one or more of the silicon nanowires has a coating including carbon.

Example embodiment 11: An integrated circuit structure includes a vertical arrangement of horizontal silicon nanowires. One or more of the silicon nanowires has a coating including carbon. A gate stack is around the vertical arrangement of horizontal silicon nanowires. A first source or drain structure is at a first end of the vertical arrangement of horizontal silicon nanowires, and a second epitaxial source or drain structure is at a second end of the vertical arrangement of horizontal silicon nanowires.

Example embodiment 12: The integrated circuit structure of example embodiment 11, wherein the vertical arrangement of horizontal silicon nanowires is above a fin.

Example embodiment 13: The integrated circuit structure of example embodiment 12, wherein a vertical spacing between the fin and a bottommost silicon nanowire of the vertical arrangement of horizontal silicon nanowires is greater than a vertical spacing between vertically adjacent silicon nanowires.

Example embodiment 14: The integrated circuit structure of example embodiment 12 or 13, wherein the fin comprises a portion of a bulk silicon substrate.

Example embodiment 15: The integrated circuit structure of example embodiment 11, 12, 13 or 14, wherein the first and second source or drain structures are first and second epitaxial source or drain structures.

Example embodiment 16: The integrated circuit structure of example embodiment 15, wherein the first and second epitaxial source or drain structures comprise silicon and germanium.

Example embodiment 17: The integrated circuit structure of example embodiment 15 or 16, wherein the first and second epitaxial source or drain structures are non-discrete first and second epitaxial source or drain structures.

Example embodiment 18: The integrated circuit structure of example embodiment 15 or 16, wherein the first and second epitaxial source or drain structures are discrete first and second epitaxial source or drain structures.

Example embodiment 19: The integrated circuit structure of example embodiment 11, 12, 13, 14, 15, 16, 17 or 18, wherein the gate stack includes a high-k gate dielectric layer and a metal gate electrode.

Example embodiment 20: A computing device includes a board, and a component coupled to the board. The component includes an integrated circuit structure including a vertical arrangement of horizontal silicon nanowires. A vertical spacing between vertically adjacent silicon nanowires is less than 6 nanometers. A gate stack is around the vertical arrangement of horizontal silicon nanowires. A first source or drain structure is at a first end of the vertical arrangement of horizontal silicon nanowires, and a second epitaxial source or drain structure is at a second end of the vertical arrangement of horizontal silicon nanowires.

Example embodiment 21: The computing device of example embodiment 20, wherein one or more of the silicon nanowires has a coating including carbon.

Example embodiment 22: The computing device of example embodiment 20 or 21, further including a memory coupled to the board.

Example embodiment 23: The computing device of example embodiment 20, 21 or 22, further including a communication chip coupled to the board.

Example embodiment 24: The computing device of example embodiment 20, 21, 22 or 23, wherein the component is a packaged integrated circuit die.

Example embodiment 25: The computing device of example embodiment 20, 21, 22, 23 or 24, wherein the component is selected from the group consisting of a processor, a communications chip, and a digital signal processor. 

What is claimed is:
 1. An integrated circuit structure, comprising: a vertical arrangement of horizontal silicon nanowires, wherein a vertical spacing between vertically adjacent silicon nanowires is less than 6 nanometers, and wherein one or more of the silicon nanowires comprises a coating comprising carbon; a gate stack around the vertical arrangement of horizontal silicon nanowires, the gate stack having a bottommost surface beneath the vertical arrangement of horizontal silicon nanowires; a first source or drain structure at a first end of the vertical arrangement of horizontal silicon nanowires, the first source or drain structure having a bottommost surface above the bottommost surface of the gate stack; and a second source or drain structure at a second end of the vertical arrangement of horizontal silicon nanowires, the second source or drain structure having a bottommost surface above the bottommost surface of the gate stack.
 2. The integrated circuit structure of claim 1, wherein the vertical arrangement of horizontal silicon nanowires is above a fin.
 3. The integrated circuit structure of claim 2, wherein a vertical spacing between the fin and a bottommost silicon nanowire of the vertical arrangement of horizontal silicon nanowires is greater than the vertical spacing between vertically adjacent silicon nanowires.
 4. The integrated circuit structure of claim 2, wherein the fin comprises a portion of a bulk silicon substrate.
 5. The integrated circuit structure of claim 1, wherein the first and second source or drain structures are first and second epitaxial source or drain structures.
 6. The integrated circuit structure of claim 5, wherein the first and second epitaxial source or drain structures comprise silicon and germanium.
 7. The integrated circuit structure of claim 5, wherein the first and second epitaxial source or drain structures are non-discrete first and second epitaxial source or drain structures.
 8. The integrated circuit structure of claim 5, wherein the first and second epitaxial source or drain structures are discrete first and second epitaxial source or drain structures.
 9. The integrated circuit structure of claim 1, wherein the gate stack comprises a high-k gate dielectric layer and a metal gate electrode.
 10. An integrated circuit structure, comprising: a vertical arrangement of horizontal silicon nanowires, wherein one or more of the silicon nanowires comprises a coating comprising carbon; a gate stack around the vertical arrangement of horizontal silicon nanowires, the gate stack having a bottommost surface beneath the vertical arrangement of horizontal silicon nanowires; a first source or drain structure at a first end of the vertical arrangement of horizontal silicon nanowires, the first source or drain structure having a bottommost surface above the bottommost surface of the gate stack; and a second source or drain structure at a second end of the vertical arrangement of horizontal silicon nanowires, the second source or drain structure having a bottommost surface above the bottommost surface of the gate stack.
 11. The integrated circuit structure of claim 10, wherein the vertical arrangement of horizontal silicon nanowires is above a fin.
 12. The integrated circuit structure of claim 11, wherein a vertical spacing between the fin and a bottommost silicon nanowire of the vertical arrangement of horizontal silicon nanowires is greater than a vertical spacing between vertically adjacent silicon nanowires.
 13. The integrated circuit structure of claim 11, wherein the fin comprises a portion of a bulk silicon substrate.
 14. The integrated circuit structure of claim 10, wherein the first and second source or drain structures are first and second epitaxial source or drain structures.
 15. The integrated circuit structure of claim 14, wherein the first and second epitaxial source or drain structures comprise silicon and germanium.
 16. The integrated circuit structure of claim 14, wherein the first and second epitaxial source or drain structures are non-discrete first and second epitaxial source or drain structures.
 17. The integrated circuit structure of claim 14, wherein the first and second epitaxial source or drain structures are discrete first and second epitaxial source or drain structures.
 18. The integrated circuit structure of claim 10, wherein the gate stack comprises a high-k gate dielectric layer and a metal gate electrode.
 19. A computing device, comprising: a board; and a component coupled to the board, the component including an integrated circuit structure, comprising: a vertical arrangement of horizontal silicon nanowires, wherein a vertical spacing between vertically adjacent silicon nanowires is less than 6 nanometers, and wherein one or more of the silicon nanowires comprises a coating comprising carbon; a gate stack around the vertical arrangement of horizontal silicon nanowires, the gate stack having a bottommost surface beneath the vertical arrangement of horizontal silicon nanowires; a first source or drain structure at a first end of the vertical arrangement of horizontal silicon nanowires, the first source or drain structure having a bottommost surface above the bottommost surface of the gate stack; and a second source or drain structure at a second end of the vertical arrangement of horizontal silicon nanowires, the second source or drain structure having a bottommost surface above the bottommost surface of the gate stack.
 20. The computing device of claim 19, further comprising: a memory coupled to the board.
 21. The computing device of claim 19, further comprising: a communication chip coupled to the board.
 22. The computing device of claim 19, wherein the component is a packaged integrated circuit die.
 23. The computing device of claim 19, wherein the component is selected from the group consisting of a processor, a communications chip, and a digital signal processor. 